Applications of advanced isotope geochemistry of hydrocarbons and inert gases to petroleum production engineering

ABSTRACT

A system and method is provided for enhancing hydrocarbon production. The method and system involve geochemistry analysis and include multiply substituted isotopolog and position specific isotope geochemistry. The method and system involve using clumped isotope and position specific isotope signatures to enhance monitoring of well and stimulation performance.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 62/111,482 filed Feb. 3, 2015 entitled APPLICATIONS OF ADVANCED ISOTOPE GEOCHEMISTRY OF HYDROCARBONS AND INERT GASES TO PETROLEUM PRODUCTION ENGINEERING, the entirety of which is incorporated by reference herein.

FIELD OF THE INVENTION

The present disclosure relates generally to the field of geochemistry including multiply substituted isotopologue and position specific isotope geochemistry. More particularly, the present disclosure describes the application of clumped isotope and position-specific isotope signatures, alongside inert gas and other stable isotope signatures, to enhance monitoring of well and stimulation performance.

BACKGROUND

This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present disclosure. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present invention. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.

Hydrocarbons are generated in the subsurface from source rocks rich in organic matter. Following initial deposition, source rocks are buried and subjected to increasing temperature and pressure with increasing burial. Hydrocarbons are generated when the source rocks reach temperatures sufficient for the thermal conversion of organic material to kerogen and then to free liquid and/or gaseous hydrocarbon phases, which is a process called source rock maturation. Upon generation, the hydrocarbons may subsequently be expulsed from the source rock and migrate in the subsurface to reservoir rocks (such as sandstones or limestones) that have sufficient porosity, structure and an adequate seal that make them capable of trapping the hydrocarbon phase(s), allowing hydrocarbons to accumulate. Alternatively, hydrocarbons may migrate to a surface location (e.g., sometimes referred to as a seep). Any hydrocarbons present in the subsurface may be preserved or they may be subjected to different forms of alteration. For example, biodegradation is the process of degradation or consumption of hydrocarbons by micro-organisms. Similarly, hydrocarbons may be thermally altered by exposure to temperatures above their thermal stability. Alternatively, hydrocarbons may be oxidized or consumed in processes, such as thermochemical sulfate reduction. In addition to hydrocarbons, non-hydrocarbon compounds (e.g., carbon dioxide CO₂, carbon monoxide CO, nitrogen N₂, hydrogen sulfide H₂S, helium He, neon Ne, argon Ar, krypton Kr, and xenon Xe) may also be present alongside hydrocarbons in subsurface accumulations. The concentration and isotopic signature of these compounds may be inherited from contact with formation waters, from mixing and interaction with other fluids in the subsurface (e.g. hydrothermal fluids, magmatic fluids) or from processes that liberate these compounds from rocks and minerals in the subsurface. Each of these processes from generation to storage and alteration influences the geochemical signature of these hydrocarbons and associated non-hydrocarbon compounds and gives rise to combined geochemical signatures that record a history of where these compounds originated and what processes they have experienced.

Evaluating and monitoring well performance, fracking and stimulation efficiency, reservoir drainage and overall production effectiveness can be challenging. Conventional tools include production logging tests, which can be costly; pressure monitoring, which may not capture full fluid flow; and tracer addition operations, which may be ineffective for tight reservoirs. Monitoring of geochemical variations on a production time-scale (e.g., time-lapse geochemistry) can be utilized, but generally does not provide advantages to the analysis if the geochemical variation between fluids from different reservoirs is slight or if there are few geochemical components to monitor (e.g., gas reservoirs).

There remains a need in the industry for apparatus, methods, and systems to identify and enhance hydrocarbon operations. In particular, conventional techniques do not properly distinguish and/or provide accurate quantitative estimates between the amount of hydrocarbon compounds (e.g., gas or liquid) that is adsorbed onto sediments in the subsurface and the amount of hydrocarbon compounds present as a free phase or between fracture and matrix derived fluids. Further, conventional techniques do not provide effective tools that can address questions relating to the extent of fracture penetration, identify wellbore integrity concerns, and accurately determine the production fetch area for a given producing well.

SUMMARY

According to disclosed aspects and methodologies, a system and method are provided for enhancing hydrocarbon production and recovery. The method and system include using geochemistry including multiply substituted isotopologue and position specific isotope geochemistry. Further, the present techniques involve the use of clumped isotope and position specific isotope signatures, alongside inert gas and other stable isotope signatures, such as noble gas signatures, to enhance monitoring of well and stimulation performance.

In one embodiment, a method for enhancing hydrocarbon production is provided. The method comprises: obtaining a plurality of hydrocarbon samples from a target subsurface interval; analyzing each of the plurality of hydrocarbon samples for geochemical signature comprising clumped isotope and/or position specific isotope geochemistry; converting each of the clumped isotope and/or position specific isotope geochemistry to temperature for each of the plurality of hydrocarbon samples; comparing the temperature of at least two of the plurality of hydrocarbon samples; determining whether gas has originated from the target interval or from a different interval; and adjusting a recovery strategy based on the determination.

In another embodiment, a system for enhancing hydrocarbon production is described. The system includes a processor; an input device in communication with the processor and configured to receive input data associated with a subsurface formation; memory in communication with the processor, the memory having a set of instructions. The set of instructions, when executed, are configured to: obtain hydrocarbon sample data for each of a plurality of hydrocarbon samples from a target subsurface interval; analyze each of the hydrocarbon sample data for a geochemical signature comprising clumped isotope and/or position specific isotope geochemistry; convert each of the clumped isotope and/or position specific isotope geochemistry to temperature for each of the plurality of hydrocarbon samples; compare the temperature of at least two of the plurality of hydrocarbon samples; determine whether gas has originated from the target interval or from a different interval; and adjust a recovery strategy based on the determination. The system further comprises an output device that outputs the adjusted recovery strategy.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other advantages of the present disclosure may become apparent upon reviewing the following detailed description and drawings of non-limiting examples of embodiments.

FIG. 1A is a side elevational view of the production of hydrocarbons in conventional or unconventional reservoirs. FIG. 1B is an expanded view illustrating free gases in the producing interval of FIG. 1A. FIG. 1C is an expanded view illustrating gases that are sorbed to surfaces in the matrix of the producing interval of FIG. 1A.

FIG. 2 is a flow diagram of an exemplary method to identify and quantify contributions from intervals not targeted for production in the flowstream using the measured multiply substituted isotopologue or position specific isotope signatures of any given hydrocarbon in accordance with an exemplary embodiment of the present techniques.

FIG. 3 is a flow diagram of an exemplary method to identify and quantify relative contributions of fracture flow gas and matrix gas in the production stream from measured multiply substituted isotopologue or position specific isotope signatures to quantify total hydrocarbons in place and develop optimal depletion strategies for the production of hydrocarbons in accordance with an exemplary embodiment of the present techniques.

FIG. 4 is a flow diagram of an exemplary method to determine the origin of stray gases in well annuli or aquifers from measured multiply substituted isotopologue or position specific isotope signatures to develop mitigation strategies if appropriate for the long term production of hydrocarbons in accordance with an exemplary embodiment of the present techniques.

FIG. 5 is a flow diagram of an exemplary method to rapidly identify leakage from producing intervals, pipeline, and or wells from measured multiply substituted isotopologue or position specific isotope signatures to develop appropriate mitigation strategies if appropriate in accordance with an exemplary embodiment of the present techniques.

FIG. 6 is a block diagram of a computer system in accordance with an exemplary embodiment of the present techniques.

DETAILED DESCRIPTION

In the following section, specific embodiments of the present techniques are described in connection with disclosed aspects and features. However, to the extent that the following description is specific to a particular aspect, technique, or a particular use, this is intended to be for exemplary purposes only. Accordingly, the invention is not limited to the disclosed aspects and techniques described below, but rather includes all alternatives, modifications, and equivalents falling within the scope of the appended claims.

Further, while for purposes of simplicity of explanation, the illustrated methodologies are shown and described as a series of blocks, it is to be appreciated that the methodologies are not limited by the order of the blocks, as some blocks can occur in different orders and/or concurrently with other blocks from that shown and described. Moreover, fewer than all the illustrated blocks may be required to implement an example methodology. Blocks may be combined or separated into multiple components. Furthermore, additional and/or alternative methodologies can employ additional, not illustrated blocks. While the figures illustrate various serially occurring actions, it is to be appreciated that various actions could occur concurrently, substantially in parallel, and/or at substantially different points in time.

Various terms as used herein are defined below. To the extent a term used in a claim is not defined below, it should be given the definition persons in the pertinent art have given that term in the context in which it is used.

As used herein, “a” or “an” entity refers to one or more of that entity. As such, the terms “a” (or “an”), “one or more”, and “at least one” can be used interchangeably herein unless a limit is specifically stated.

As used herein, the terms “comprising,” “comprises,” “comprise,” “comprised,” “containing,” “contains,” “contain,” “having,” “has,” “have,” “including,” “includes,” and “include” are open-ended transition terms used to transition from a subject recited before the term to one or more elements recited after the term, where the element or elements listed after the transition term are not necessarily the only elements that make up the subject.

As used herein, the term “exemplary” means exclusively “serving as an example, instance, or illustration.” Any embodiment described herein as exemplary is not to be construed as preferred or advantageous over other embodiments.

As used herein, the term “fracture flow” refers to the movement of reservoir fluids through natural or induced fractures or fracture networks in the rock.

As used herein, the term “hydrocarbons” are generally defined as molecules formed primarily of carbon and hydrogen atoms such as oil and natural gas. Hydrocarbons may also include other elements or compounds, such as, but not limited to, halogens, metallic elements, nitrogen, oxygen, sulfur, hydrogen sulfide (H₂S), and carbon dioxide (CO₂). Hydrocarbons may be produced from hydrocarbon reservoirs through wells penetrating a hydrocarbon containing formation. Hydrocarbons derived from a hydrocarbon reservoir may include, but are not limited to, petroleum, kerogen, bitumen, pyrobitumen, asphaltenes, tars, oils, natural gas, or combinations thereof. Hydrocarbons may be located within or adjacent to mineral matrices within the earth, termed reservoirs. Matrices may include, but are not limited to, sedimentary rock, sands, silicilytes, carbonates, diatomites, and other porous media.

As used herein, “hydrocarbon production” refers to any activity associated with extracting hydrocarbons from a well or other opening. Hydrocarbon production normally refers to any activity conducted in or on the well after the well is completed. Accordingly, hydrocarbon production or extraction includes not only primary hydrocarbon extraction but also secondary and tertiary production techniques, such as injection of gas or liquid for increasing drive pressure, mobilizing the hydrocarbon or treating by, for example chemicals or hydraulic fracturing the wellbore to promote increased flow, well servicing, well logging, and other well and wellbore treatments.

As used herein, the term “isotope” refers to one of two or more atoms with the same atomic number but with different numbers of neutrons. Hydrocarbon molecules may contain a variety of isotopes. Hydrocarbon molecules contain both carbon and hydrogen atoms. Carbon can be present in the molecule as one of two stable isotopes: ¹²C, which has 6 protons and 6 neutrons (shown herein as C); and, in much lower concentrations, ¹³C, which has 6 protons and 7 neutrons. Similarly, hydrogen can be present in a molecule as one of two stable isotopes: H, which contains 1 proton but no neutron; and, in much lower concentrations, Deuterium (D), which has 1 proton and 1 neutron.

As used herein, the term “signatures” refers to the relative abundances, concentrations and/or ratios of various elements, isotopes, positions within a compound and isotopologues of a given species.

As used herein, the term “isotopologue” refers generally to molecules that have the same chemical composition, but have a different isotopic signature. For example, methane contains one atom of carbon and four atoms of hydrogen. Each atom in the methane structure can contain one of the two stable isotopes of that atom, and as such there are ten isotopologues of methane.

As used herein, the term “matrix flow” refers to the movement of reservoir fluids through the rock fabric.

As used herein, the term “multiply substituted isotopologue” refers generally to an isotopologue that contains at least two rare isotopes in its structure. For example, a multiply substituted methane isotopologue contain one ¹³C atom and one D atom, or at least 2 D atoms in the absence of a ¹³C atom.

As used herein, the term “clumped isotopologue” refers generally to an isotopologue that contains at least two rare isotopes that share a common chemical bond in its structure. For example, a clumped isotopologue of methane contains one ¹³C atom that shares a chemical bond with at least one D atom.

As used herein, the term “position specific isotope signature” refers generally to a compound that has multiple chemically or structurally distinct positions for a rare isotope to reside. For example, a position specific isotope signature in propane could refer to the position of the ¹³C atom, which can be positioned either at the center of the compound or one of the end positions, or the position of the D atom, which can be attached to either a central or end position carbon.

As used herein, the term “stochastic distribution” refers generally to a system where the stable isotopes in a given population of molecules are distributed randomly among all possible isotopologues of a given species. This stochastic distribution is the reference frame from which deviations are measured and is used to provide a baseline to identify anomalies that may be associated with secondary isotope exchange processes.

As used herein, the term “spike” refers generally to the addition of a compound that has an exotic signature that does not occur naturally at such high concentrations in nature. For example, a spike could take the form of pure ¹³CD₄, the least abundant clumped isotopologue of methane which is not thought to be measurable at natural abundance, but could be measured if present at high concentrations.

The present techniques relate to geochemistry, and more particularly, multiply substituted isotopologue and position specific isotope geochemistry. In certain aspects, the present techniques involve the application and use of clumped isotope and position specific isotope signatures, alongside inert gas and other stable isotope signatures, to enhance monitoring of well and stimulation performance. The technology is based on the identification of these signatures to provide a unique characterization of fluids derived from different reservoir units, and/or different portions of a reservoir, and determining when and how much mixing could occur between those fluids. A unique clumped isotope and position specific signature for a reservoir fluid could be related to different sources, maturity, alteration, reservoir properties, and/or physical association within a reservoir (adsorbed versus pore space); a unique reservoir inert gas signature could be related to different proportions of hydrocarbon versus water. Integrated with other geochemical data, such information may provide more quantitative constraints on the source of hydrocarbons (gaseous and liquid) to enhance engineering solutions to ensure long term production of hydrocarbons.

According to aspects of the disclosed methodologies and techniques, the multiply substituted isotopologue or position specific isotope effects or signatures of single or numerous co-existing isotopologues of hydrocarbons can be integrated with results from other geochemical approaches that incorporate the relative or absolute concentration and isotopic signature of other hydrocarbon and non-hydrocarbon compounds (e.g., carbon dioxide (CO₂), carbon monoxide (CO), nitrogen (N₂), hydrogen sulfide (H₂S), helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe)) to improve monitoring of well and stimulation performance. The technology is based on the identification of these signatures to provide a unique characterization of fluids derived from different reservoir units, and/or different portions of a reservoir, and determine when and how much mixing could occur between those fluids. A unique clumped isotope and position specific signature for a reservoir fluid could be related to different sources, maturity, alteration, reservoir properties, and/or physical association within a reservoir (adsorbed versus pore space). A unique reservoir inert gas signature could be related to, amongst other things, different relative proportions of hydrocarbon versus water, contributions from the radiogenic decay of crustal minerals or magmatic fluids, modes of transport or movement of fluids (e.g. advective transport in matrix versus diffusive transport in tight rocks), physical fractionating processes such as sorption, and phase changes (e.g., liquid drop out and gas cap formation). In contrast, a unique non-hydrocarbon gas signature could arise from contributions of compounds, such as CO₂, N₂ and H₂S, from organic maturation or thermal alteration of minerals (temperature related), from magmatic fluids or other sources.

Techniques capable of providing this information may provide quantitative constraints on sorbed versus free gas or fracture versus matrix fluids and address problems related to fracture penetration, wellbore integrity, and production fetch area for optimal long-term hydrocarbon production strategies, to develop enhanced engineering solutions for more effective and efficient fracture penetration in conventional and unconventional reservoirs, to provide rapid identification and mitigation of well bore integrity failures or issues related to stray gas presence in aquifers and predict the production fetch area and as such more accurately quantify the estimated ultimate recovery of hydrocarbons for any given producing well.

In one or more embodiments, the present techniques may include combining multiply substituted isotopologue signatures and position specific isotope geochemistry of hydrocarbon compounds (e.g., CH₄, C₂H₆, and C₃H₈) and non-hydrocarbon compounds (e.g., H₂S, CO₂, N₂, He, Ne, Ar, Kr, and Xe) with elemental, molecular and isotopic signatures obtained from gas, oil, water and fluid inclusion samples.

The use of multiply substituted isotopologue and position specific isotope geochemistry may provide constraints on the temperature at which particular processes occur in hydrocarbon systems. When combined and integrated with traditional geochemical techniques, such as molecular (e.g., methane, ethane, carbon dioxide, nitrogen), bulk (e.g., mixtures of gases), stable isotope geochemistry (e.g., carbon, hydrogen, nitrogen, sulfur) of hydrocarbon and non-hydrocarbon gases, molecular geochemistry of oils (e.g., saturate and aromatic compounds), physical measurements (e.g., pressure, volume, and temperature (PVT)), and results from engineering tests (e.g., production logging test (PLT), or temperature logging), then these techniques provide enhancements to existing technologies to quantitatively determine the origin of hydrocarbons (e.g., produced or leaked). For example, using these technologies one can discriminate between production dominated by fracture flow and that dominated by free phase hydrocarbons or desorption of hydrocarbons from mineral or organic surfaces. In addition, contributions of hydrocarbons originating from multiple reservoir formations can be identified and quantified. For example, when artificial fractures penetrate through sealing strata and into other hydrocarbon bearing formations, or where artificial fractures intersect with natural fractures that result in contributions from other reservoirs. In addition, these technologies may be used to constrain the source of hydrocarbons within well bores when wellbore integrity is under investigation or in aquifers when present at unusually high concentrations and contamination is suspected. The technology therefore provides a mechanism to alter engineering practices and production strategies to maximize the volume and quality of hydrocarbon ultimately produced and also to mitigate any issues associated with the production of hydrocarbons if this is shown to be resulting in the leakage of hydrocarbons in the near well bore area.

Multiply substituted isotopologue geochemistry is based on the variation in the distribution of isotopes within a molecule that gives rise to molecules that are identical in their elemental composition, but that may differ in the isotopic composition of individual atoms within that molecule. These species are called isotopologues. For example, there are three isotopologues of nitrogen (e.g., ¹⁴N₂, ¹⁵N¹⁴N and ¹⁵N₂). An isotopologue in which two or more rare isotopes are present in close proximity (isotopic “clumps”) is called a multiply-substituted isotopologue or clumped isotope (e.g., ¹⁵N₂). The hydrocarbon isotopologues involve hydrocarbon compounds that have natural isotopes of ¹²C, ¹³C, ¹H, or H (i.e., deuterium or D). ¹²C represents about 98.93 mole percent (mol. %) of the total carbon on Earth, while ¹³C forms the remaining 1.07 mol. %. Similarly, the isotopic abundance of ¹H on earth is 99.985 mol. % while D has an abundance of 0.015 mol. %. Common volatile hydrocarbons have large numbers of isotopologues even considering only the stable isotopes (e.g., methane has 10; ethane has 36; propane has 216). Common isotopologues of methane for example include ¹³C¹H₃D or ¹²C¹H₄. In addition to the number of rare isotopes, the distribution of isotopes in the molecule can also provide information. For example, in a linear hydrocarbon compound with three carbon atoms, the rare isotope can take either a central or terminal (end of the molecule) position. Similarly, rare isotopes of hydrogen can occupy different positions. As the size of the hydrocarbon compound increases, the number of positions that these rare isotopes can be situated increases. This effect is called the position specific isotope signature or effect, or isotopomer geochemistry.

The multiply substituted isotopologue and the position specific isotope signature of any molecule is a function of (i) temperature-independent randomly populated processes (e.g., stochastic distribution) and (ii) other non-random mass fractionating processes. The stochastic distribution of any set of isotopologues can be determined from the bulk isotope signatures of the species from which it derives. For example, determining the stochastic distribution of isotopologues for methane involves knowledge of the ¹³C and D signatures of methane. At equilibrium, a non-stochastic distribution may result from thermodynamic differences between the different isotopologues. Under non-equilibrium conditions, the non-random processes may be temperature-time dependent isotopic exchange reactions in some hydrocarbons. For example, multiply substituted isotopologue signatures in methane appear to provide equilibrium gas generation temperatures See, e.g., Stolper et al., Formation temperatures of thermogenic and biogenic methane, Science, 344, p. 1500-1503 (2014). Additional equilibrium or non-equilibrium kinetic isotope exchange processes may also influence the signatures in some hydrocarbon species. These processes may include, but are not limited to, biodegradation, secondary thermal cracking of hydrocarbons, thermochemical oxidation or reduction reactions, mixing or diffusion, physical processes such as sorption or desorption, or transport processes such as diffusion and advection. These processes may differ in their relative magnitude of the impact on the multiply substituted isotopologue and/or position specific isotope signatures. These processes result in changes in the concentrations and isotopic signatures of non-hydrocarbon compounds. By measuring the clumped and position specific isotope signatures of multiple hydrocarbon compounds that may be sensitive to different parameters, and through the integration of this information with other complimentary geochemical systems (such as, the noble gases that record physical processes; such as, diffusion, advection, and mixing processes amongst other things), one can determine the processes controlling these signatures and quantify the extent of this effect on the sample. Such information can then be used to quantify gas production from different sources of gas (e.g., sorbed, free gas, matrix gas, fracture gas) and determine the origin of stray gases in the immediate vicinity of a producing well. In addition, the introduction of a geochemical spike with a very exotic clumped isotope signature can be used to more rapidly detect leakage to these locations. Various aspects of the present techniques are described further in FIGS. 1 to 6.

FIG. 1A is a side elevational diagram 100 of the production of hydrocarbons in conventional or unconventional reservoirs, which is located below the surface 101. In this diagram 100, different sources of hydrocarbon fluids, flow by arrows 130, 132, 134, 136 and 138, are shown and produced in the well bore 102 to the surface and pipelines 103. These sources of hydrocarbons include hydrocarbons that reach the well bore through artificially induced fractures 107 in the producing strata or interval 104, or through fractures that extend into a different hydrocarbon bearing interval or strata 105. Gases may initially be present as a free gas phase in the producing interval, as shown in the expanded area 108 illustrated in FIG. 1B, or may be initially sorbed to surfaces in the matrix, as shown by expanded area 110 illustrated in FIG. 1C, until conditions change and they are liberated. Gas production may be dominated by flow from this matrix in the expanded areas 108 and 110, or may be dominated by from flow from fractures 107. Hydrocarbons may also leak from the producing well bore 102 into the well annulus 114. Understanding the source and flow of hydrocarbons is useful to prevent movement towards aquifers, such as aquifer 116, which may be a thousand feet or more from the producing interval 104.

Understanding the penetration depth and effectiveness of fractures propagated during fracking into tight oil and gas reservoirs may provide needed information that may be utilized to enhance hydrocarbon production. For example, some fractures may penetrate too far, and thereby breach the sealing horizons and penetrate into hydrocarbon-poor, water-rich units, and/or penetrate into different hydrocarbon-rich units. These fractures may be detected in produced fluids by a shift in the clumped isotope, position-specific, and/or inert gas/isotope signature due to mixing with fluids outside the principal reservoir. Such breaching may reduce production efficiency and could even lead to contamination of nearby intervals. The present techniques provide a mechanism for early recognition and monitoring of the extent of seal breach thereby allowing for optimized fracking operations. Even if a sealing unit is not breached, if enough differences exist in signatures throughout the target reservoir, a shift in signatures for produced fluids post-fracking may provide a mechanism to monitor and optimize fracture penetration as well as modeling reservoir drainage. Applications related to the penetration or breaching of seals or baffles may also enhance production efficiency and monitoring of high permeability (conventional) reservoirs.

FIG. 2 is a flow diagram 200 of an exemplary method to identify and quantify contributions of gases from different gas bearing intervals from the measured multiply substituted isotopologue or position specific isotope signatures of any given hydrocarbon in accordance with an exemplary embodiment of the present techniques. In this diagram 200, this approach may be used to identify compounds whose multiply substituted isotopologue signature and/or position specific isotope signatures are controlled only or primarily by temperature (e.g., an equilibrium signature that is predictable from molecular modeling). That is, the approach may identify and quantify contributions of gases from different gas bearing intervals.

The method begins at block 202. In block 202, a sample of hydrocarbons is obtained from the target subsurface interval(s). The target subsurface interval may include a specific production interval or region within the subsurface formation. The sample may be obtained during drilling operations or at a first period of time prior to the subsequent samples below. This sample can be in the form of oil and/or gas obtained from within the wellbore or during flowing of the well (e.g., the initial flowing of well). Alternatively, a gas sample could be collected from mud circulating in the well bore.

At block 204, the sample is analyzed for geochemical signature comprising clumped isotope and/or position specific isotope geochemistry. The sample(s) geochemical signature may include multiply substituted isotopologue and/or position specific isotope geochemistry information. If methane, the primary chemical component of natural gases, is used as an example, it is possible to investigate the potential of forming the clumped doubly substituted isotopologue ¹³CH₃D, and the doubly substituted isotopologue ¹²CH₂D₂. This analysis may also include a variety of geochemical signatures comprising bulk composition, isotopic signatures of groups of elements, such as, the noble gases, molecular geochemistry, which may be used to provide additional information, such as, mass of water that has interacted with the fluid or to identify processes, such as mixing. The sample may be analyzed for its multiply substituted isotopologue and or isotope position specific signature. The measurement of the absolute abundance of isotopologues or position of interest for any given hydrocarbon involves knowledge of the molecular mass or absorption spectra at which they are present, and hence involves knowledge of the actual identity of each possible isotopologue for that species. Measurement of the abundance of each isotopologue or fragment can be conducted using multiple techniques, such as, mass spectrometry and/or laser-based spectroscopy.

Then, at block 206, the multiply substituted isotopologue and/or position specific isotope signature is converted to temperature. Temperature is an equilibrium signature that can be predicted by molecular modeling of equilibrium concentrations of multiply substituted isotopologue or positional effects, or may be determined empirically by measurements of signatures of a given hydrocarbon compound at different temperatures either in the presence or absence of a catalyst to accelerate equilibrium. Different hydrocarbon species have different rates of equilibration of their multiply substituted isotopologue and position specific effects. For example, the ¹³CH₃D isotopologue in methane may record methane generation temperature (See, e.g., Stolper et al., Science (2014), which is hereby incorporated by reference) and preserves the signature even when exposed to different temperatures during migration or uplift of the sediments in which the methane is contained.

In block 208, another sample of hydrocarbons is obtained. This sample may be obtained during production of hydrocarbons or at a later time than the first sample in block 202. This sample can be in the form of oil and/or gas obtained from within the wellbore or at a surface location, such as, a well head or separator.

In block 210, the samples geochemical signature, which may include multiply substituted isotopologue and/or position specific isotope geochemistry, may be analyzed.

Then, in block 212, the multiply substituted isotopologue and/or position specific isotope signature is converted to temperature as in block 206 above.

In block 214, temperatures of produced gas are compared with that determined for target interval. For example, the multiply substituted isotopologue or position specific based temperature of the produced gas determined in block 212 is compared to that of the targeted subsurface interval determined in block 206.

At block 216, a determination of whether gas has originated from intended producing interval or if there are contributions from deeper or shallower sources is performed. For example, it is determined through comparison of temperatures in block 214 whether a component of the gas present in the production stream originates from a single or from multiple gas bearing intervals. In this instance, a gas sample taken from an interval where the ambient temperature is 100° C. would give rise to a clumped isotope signature of 100° C. if it is uniquely from that interval. In contrast, a signature of significantly above or below 100° C. suggests contribution from gas bearing strata above or below.

At block 218, development and production strategies may be developed or refined. The strategies may be used to mitigate the contribution in the current or future wells by decreasing fracture penetration, for example.

In block 220, the strategies may be used to produce hydrocarbons. That is, based on the comparison, drilling of a well may be performed to provide access to the hydrocarbon accumulation. Further, the production may include installing or modifying a production facility for the production of hydrocarbons from the production intervals that provide access to the hydrocarbons in the subsurface formation. The production facility may include one or more units to process and manage the flow of production fluids, such as hydrocarbons and/or water, from the formation. To access the production intervals, the production facility may be coupled to a tree and various control valves via a control umbilical, production tubing for passing fluids from the tree to the production facility, control tubing for hydraulic or electrical devices, and a control cable for communicating with other devices within the wellbore. The strategy may adjust the well locations, fracture depths and patterns, etc.

Further, as another example, it is useful for reserves estimation and well performance prediction to understand the physical origin of hydrocarbons. Both matrix and fracture fluids can contribute to production, as can sorbed and free fluids. Production strategies can differ significantly for these different fluids and it is therefore useful to be able to recognize and monitor the contributions of each. Clumped isotope and position-specific isotope signatures can be affected by sorption and may therefore reflect contribution of adsorbed versus free gas. Signatures for hydrocarbons produced predominantly from fractures may reflect more mixing than fluids produced predominantly from matrix hydrocarbons.

Beneficially, this method provides an enhancement in the production and exploration of hydrocarbons. In particular, the method may be utilized to enhance drilling operations and/or production to provide more information about the presence and location of hydrocarbon sources. Further, the integration of this information with seismic data with gravity, magnetics, and acoustic data from other measurements, subsurface model or other information may provide additional insights to enhance the operations.

This combined geochemical signature comprising noble gases and clumped isotopes can also be used to provide an enhancement in the production and exploration of hydrocarbons by allowing discrimination between fracture and matrix-dominated flow regimes. In particular, the method may be utilized to enhance production operations. Further, the integration of this information with seismic data with gravity, magnetics, and acoustic data from other measurements, subsurface model or other information may provide additional insights to enhance the operations.

FIG. 3 is a flow diagram 300 of an exemplary method to identify and quantify relative contributions of fracture flow gas and matrix gas in the production stream from measured multiply substituted isotopologue or position specific isotope signatures to quantify total hydrocarbons in place and develop optimal depletion strategies for the production of hydrocarbons determine charge timing of hydrocarbons in an accumulation in accordance with an exemplary embodiment of the present techniques. In this diagram 300, the method may be used to convert measured multiply substituted isotopologue or position specific isotope signatures into a signature associated with fracture flow, which is likely to be an equilibrium signature that does not experience a kinetic isotope effect, or matrix flow, which may exhibit a kinetic isotope effect because of diffusive fractionation that may occur during production of gas dominated by matrix flow. This is because lighter compounds (fewer rare isotope substitutions) can move faster through a matrix compared with heavier compounds (e.g., clumped isotopes). These different sources of gas may also exhibit difference in the noble gas signature associated with physical, transport-related fractionation differences between fracture flow and matrix flow. Further, this method may be used to identify changes in the relative contributions of these different sources of gas over the course of production and a shift from, for example, fracture flow dominated during initial stages of production to more matrix gas dominated production as pressure decreases in the reservoir and most of the easily accessible fracture gas has been produced. That is, the method determines the relative contributions of fracture flow versus matrix flow in production stream and changes during production.

The method begins at block 302. In block 302, samples of hydrocarbons are collected at different stages of production. Similar to block 202, this sample may be in the form of oil and/or gas obtained from the subsurface or oil and/or gas at a surface location.

At block 304, samples for geochemical signature comprising clumped isotope/position specific isotope geochemistry and noble gas geochemistry are analyzed. The samples geochemical signature, which may include multiply substituted isotopologue and/or position specific isotope geochemistry, may be analyzed as in block 204. This analysis may also comprise noble gas analysis.

Then, at block 306, the difference in the noble gas signature and clumped isotope/position specific signature for at least one hydrocarbon compound of interest associated with fracture flow vs matrix flow in the produced gas sample may be determined. That is, the multiply substituted isotopologue and/or position specific isotope signature of at least one hydrocarbon compound of interest and/or noble gas signature of the sample is interpreted in the context of that likely representative of fracture gas or matrix gas dominated. This can be done through comparison of the sample data with that obtained by experiment where a signature of matrix gas is initially constrained. This can be done, for example, by taking a gas mixture containing hydrocarbons and other compounds and introducing it in to a sample vessel containing a solid with a low porosity or permeability and increasing the pressure in the sample container. Aliquots of the sample are then analyzed as the pressure is decreased to determine the fingerprint of clumped isotopes/position specific effects and other compounds such as the noble gases as gas is progressively released from the matrix. For example, it has been shown that light noble gases, such as, helium have a small enough molecular size that they can access very small pores within a matrix. It is therefore expect that fracture gases may be relatively depleted in these light noble gases, and that the concentration of helium may increase with increasing contribution of matrix gas to the produced gas.

In block 308, the clumped isotope and/or position specific signatures and noble gas signatures during production are monitored for changes in the relative contribution of matrix vs fracture sourced gas. The produced gas samples are routinely analyzed over production timescales to monitor changes in the relative contributions of fracture gas versus matrix gas and how this changes as a function of total gas produced or other variables such as reservoir pressure.

Then, in block 310, production strategies to enhance total recovery of hydrocarbons are developed or refined. This information is used to develop or refine production strategies for any given well in the same or analogous hydrocarbon system when some estimate of reservoir pressure or other controlling variable is known or can be predicted. This way, it may be possible to access a great volume of hydrocarbons by, for example, more slowly decreasing reservoir pressure to access a greater proportion of matrix gas relative to fracture gas or vice versa.

At block 312, this information or strategies is used to produce hydrocarbons. The use may be similar to that noted in block 220 of FIG. 2.

As another example, monitoring of the clumped isotope and/or position specific signatures can also be used to enhance identification of the source of “stray gas” when unusually high concentrations of hydrocarbons are found in unexpected locations. This may include locations, such as, well annuli or aquifers. If the casing or cement for a well is compromised, reservoir fluids may leak in to the well annuli or out into the surrounding strata and/or to the surface. Clumped isotope and/or position-specific isotope signatures can enhance identification of the source of leaking fluids (e.g., natural versus well-induced). By the same notion, leakage in the annulus of a well can potentially be traced via these signatures to the reservoir source (e.g., target reservoir versus shallow biogenic gas reservoirs).

In addition to the applications described above, the combined geochemical signature comprising noble gases and clumped isotopes can also be used to trace the origin of gas found within or surrounding well annuli. The integration of this information with well data and other measurements can help optimize current production, as well as enhance future drilling operations and mitigate leakage if appropriate.

FIG. 4 is a flow diagram 400 of an exemplary method to determine the origin of stray gases in well annuli or aquifers from measured multiply substituted isotopologue or position specific isotope effect signatures in accordance with an exemplary embodiment of the present techniques. In this diagram 400, this information can be used to enhance development of mitigation strategies if appropriate for the long term production of hydrocarbons.

The method begins in block 402. At block 402, a sample of hydrocarbons is obtained from each interval intended to be produced during drilling or in production test. This sample can be in the form of hydrocarbons in the well bore, during well testing at a surface location, or of hydrocarbons present in rock samples taken during drilling. This may be obtained in a manner similar to the blocks noted above.

Then, at block 404, the samples are analyzed for geochemical signature comprising clumped isotope/position specific isotope geochemistry. The sample analysis for the multiply substituted isotopologue and/or position specific isotope geochemical signatures of at least one hydrocarbon of interest may be performed in a manner noted above.

At block 406, samples are collected of stray fluids present in aquifer and/or well annuli where present. The sample is collected when elevated concentrations of hydrocarbons are suspected or found in well annuli or other strata (e.g., in aquifers) and the origin of this gas is unknown.

In block 408, the sample is analyzed for the multiply substituted isotopologue and/or position specific isotope geochemical signatures of at least one hydrocarbon of interest. This analysis may be similar to that performed in block 404.

Then, in block 410, stray fluid geochemical signatures are compared with production interval signatures. That is, the signature determined in block 408 is compared with those obtained in block 404.

In block 412, the likely source of stray fluids is determined. For example, the comparison of signatures in block 410 is used to determine whether the elevated concentrations of hydrocarbons present in unexpected locations originated from the producing intervals characterized in 404. This can be done through direct comparison of signatures. Alternatively, signatures determined in 404 may have been altered as a result of biogeochemical processes operating in the new environment. The comparison should consider possible processes, for example, biodegradation, and how these may occur to ultimately change the signature of the producing interval. If it is shown that the hydrocarbons did indeed originate from the producing interval, the mechanism of escape must be determined. This can be done using traditional techniques such as acoustic based approaches where a microphone is placed down a wellbore and is used to listen for leakage of hydrocarbons through the well bore.

Alternatively, the cement bond log can be used to examine for potential areas of poor cement isolation of the annular space between the production casing and the drill hole. Temperature and differential temperature logs can be used to search for areas of leakage. Radioactive tracer surveys may be used in some cases. Pressure integrity tests can be run on the well. The time-pressure history of the various annular spaces in the well can be reviewed to determine if pressure loss was observed (and in which annular space). The well may be equipped with fiber optic cables such as Distributed Temperature Sensing (DTS) or Distributed Acoustical Sensing (DAS) to track locations along the well where fluids may be flowing.

At block 414, the information is used to develop mitigation strategies if appropriate. For example, the location information determined in block 412 is then used in block 414 to develop mitigation strategies to prevent further leakage of hydrocarbons in the given well. This information may also be used to change facility infrastructure in other wells to ensure that a similar process does not occur elsewhere.

At block 416, this information or strategies is used to produce hydrocarbons. The use may be similar to that noted in block 220 of FIG. 2.

In addition to the applications described above, the differences in clumped isotope signatures can be exaggerated through introduction of exotically clumped species (not naturally occurring). This allows for easy identification of hydrocarbon flow and reaction or physical processes.

Because in some cases end-member signatures may not be unique in a given location, it can be difficult to determine the source of hydrocarbons with any confidence when leakage is suspected. An alternative approach may be to introduce an exotic spike to producing intervals or to pipelines to enable rapid and unambiguous identification of leakage from these intervals to the surrounding environment.

FIG. 5 is yet another example of how multiply substituted isotopologue signatures and position specific isotope signatures for at least one hydrocarbon compound of interest may be used to rapidly identify leakage from producing intervals, pipeline, and or wells and to ultimately develop appropriate mitigation strategies if appropriate. In this diagram 500, information on the presence of exotic clumped isotope or position specific effect signatures in the surrounding environment that are introduced to producing intervals is used as a mechanism to rapidly identify leakages to the surrounding environment.

The method begins in block 502. At block 502, an exotic clumped isotope or position specific spike is introduced in to producing intervals, flow streams and/or pipelines. This spike should comprise signatures that may not be observed in such high concentrations in nature. Such spikes could include isotopologues such as ¹³CD₄ for methane which, when not spiked, has a natural abundance of 10⁻¹⁷ to 10⁻¹⁹, and is not detectable using current techniques.

Then, at block 504, samples are collected of stray fluids present in aquifer/well annuli where present. For example, a sample may be collected when elevated concentrations of hydrocarbons are suspected or found in well annuli or other strata (e.g. in aquifers) and the origin of this gas is unknown as in block 404.

In block 506, stray fluid samples are analyzed for geochemical signature comprising clumped isotope/position specific isotope geochemistry. The sample is analyzed for the multiply substituted isotopologue and/or position specific isotope geochemical signatures of at least one hydrocarbon of interest as in block 404.

Then, in block 508, a determination whether contributions of fluids spiked with exotic clumped isotope signature are present. That is, it is determined whether the signature determined in block 506 contains evidence of the presence of the exotic spike introduced in block 502.

In block 510, the presence or absence of the spike determines whether hydrocarbons that were given the spike have leaked in to the surrounding environment. If it is shown that the hydrocarbons did indeed originate from the producing interval, the mechanism of escape must be determined. This can be done using traditional techniques such as acoustic based approaches where a microphone is placed down a wellbore and is used to listen for leakage of hydrocarbons through the well bore. Alternatively, the cement bond log can be used to examine for potential areas of poor cement isolation of the annular space between the production casing and the drill hole. Temperature and differential temperature logs can be used to search for areas of leakage. Radioactive tracer surveys may be used in some cases. Pressure integrity tests can be run on the well. The time-pressure history of the various annular spaces in the well can be reviewed to determine if pressure loss was observed (and in which annular space). The well may be equipped with fiber optic cables such as Distributed Temperature Sensing (DTS) or Distributed Acoustical Sensing (DAS) to track locations along the well where fluids may be flowing.

In block 512, the information is used to develop mitigation strategies if appropriate. For example, the location information determined in block 510 is then used to develop mitigation strategies to prevent further leakage of hydrocarbons in the given well. This information may also be used to change facility infrastructure in other wells to ensure that a similar process does not occur elsewhere.

FIG. 6 is a block diagram of a computer system 600 in accordance with an exemplary embodiment of the present techniques. A central processing unit (CPU) 602 is coupled to system bus 604. The CPU 602 may be any general-purpose CPU, although other types of architectures of CPU 602 (or other components of exemplary system 600) may be used as long as CPU 602 (and other components of system 600) supports the inventive operations as described herein. The CPU 602 may execute the various logical instructions according to various exemplary embodiments. For example, the CPU 602 may execute machine-level instructions for performing processing according to the operational flow described above.

The computer system 600 may also include computer components such as a random access memory (RAM) 606, which may be SRAM, DRAM, SDRAM, or the like. The computer system 600 may also include read-only memory (ROM) 608, which may be PROM, EPROM, EEPROM, or the like. RAM 606 and ROM 608 hold user and system data and programs, as is known in the art. The computer system 600 may also include an input/output (I/O) adapter 610, GPU(s) 614, a communications adapter 622, a user interface adapter 624, and a display adapter 618. The I/O adapter 610, the user interface adapter 624, and/or communications adapter 622 may, in certain embodiments, enable a user to interact with computer system 600 in order to input information.

The I/O adapter 610 preferably connects a storage device(s) 612, such as one or more of hard drive, compact disc (CD) drive, floppy disk drive, tape drive, etc. to computer system 600. The storage device(s) may be used when RAM 606 is insufficient for the memory requirements associated with storing data for operations of embodiments of the present techniques. The data storage of the computer system 600 may be used for storing information and/or other data used or generated as disclosed herein. The communications adapter 622 may couple the computer system 600 to a network (not shown), which may enable information to be input to and/or output from system 600 via the network (for example, the Internet or other wide-area network, a local-area network, a public or private switched telephony network, a wireless network, any combination of the foregoing). User interface adapter 624 couples user input devices, such as a keyboard 628, a pointing device 626, and the like, to computer system 600. The display adapter 618 is driven by the CPU 602 to control, through a display driver 616, the display on a display device 620. Information and/or representations pertaining to a portion of a supply chain design or a shipping simulation, such as displaying data corresponding to a physical or financial property of interest, may thereby be displayed, according to certain exemplary embodiments.

The architecture of system 600 may be varied as desired. For example, any suitable processor-based device may be used, including without limitation personal computers, laptop computers, computer workstations, and multi-processor servers. Moreover, embodiments may be implemented on application specific integrated circuits (ASICs) or very large scale integrated (VLSI) circuits. In fact, persons of ordinary skill in the art may use any number of suitable structures capable of executing logical operations according to the embodiments.

As an example, machine-readable logic or code may be used or executed with a computing system, such as computing system 600 of FIG. 6. The code or a set of instructions is provided enhancing hydrocarbon production, which may include analyzing hydrocarbon samples for geochemical signature comprising clumped isotope and/or position specific isotope geochemistry and noble gas geochemistry. When executed or applied with a computer system, such as computer system 600, code or set of instructions is configured to: obtain hydrocarbon sample data for each of a plurality of hydrocarbon samples from a target subsurface interval; analyze each of the plurality of hydrocarbon samples for geochemical signature comprising clumped isotope and/or position specific isotope geochemistry; convert each of the clumped isotope and/or position specific geochemistry to temperature for each of the plurality of hydrocarbon samples; compare the temperature of at least two of the plurality of hydrocarbon samples; determine whether gas has originated from the target interval or from a different interval; and adjust a recovery strategy based on the determination; and display or store the adjusted recovery strategy.

It should be understood that the preceding is merely a detailed description of specific embodiments of the invention and that numerous changes, modifications, and alternatives to the disclosed embodiments can be made in accordance with the disclosure here without departing from the scope of the invention. The preceding description, therefore, is not meant to limit the scope of the invention. Rather, the scope of the invention is to be determined only by the appended claims and their equivalents. It is also contemplated that structures and features embodied in the present examples can be altered, rearranged, substituted, deleted, duplicated, combined, or added to each other. 

What is claimed is:
 1. A method for enhancing hydrocarbon production comprising: obtaining a first sample comprising hydrocarbons from a target subsurface interval of a reservoir; analyzing the first sample for a geochemical signature, wherein the geochemical signature comprises a clumped isotope signature and/or a position specific isotope signature for a hydrocarbon compound of interest in the first sample; converting the clumped isotope signature and/or the position specific isotope signature of the hydrocarbon compound of interest to a temperature for the first sample; obtaining a second sample comprising hydrocarbons from the target subsurface interval of the reservoir, wherein the second sample is obtained at a time later than the first sample; analyzing the second sample for a geochemical signature, wherein the geochemical signature comprises a clumped isotope signature and/or a position specific isotope signature for the hydrocarbon compound of interest in the second sample; converting the clumped isotope signature and/or the position specific isotope signature of the hydrocarbon compound of interest to a temperature for the second sample; comparing the temperatures of the first and second samples; determining whether the hydrocarbons in the second sample originated from the target subsurface interval or from a different interval in the reservoir, wherein the determination is based at least in part on the comparison of the temperatures of the first and second samples; adjusting a recovery strategy for the reservoir based on the determination; and producing hydrocarbons from the reservoir based on the adjusted recovery strategy.
 2. The method of claim 1, wherein analyzing the first or second sample for the geochemical signature further comprises determining a noble gas signature.
 3. The method of claim 2, further comprising determining differences between the noble gas signatures for the first and second samples.
 4. The method of claim 1, wherein the determination involves analyzing each of the first and second samples to identify a source contribution for each of the first and second samples.
 5. The method of claim 1, further comprising monitoring the geochemical signature of a plurality of samples during production for changes in the source contribution for each of the plurality of samples.
 6. The method of claim 5, wherein the source contribution comprises determining fracture flow versus matrix flow.
 7. The method of claim 6, wherein fracture flow is movement of reservoir fluids through natural or induced fractures or fracture networks in the rock and matrix flow is movement of reservoir fluids through the rock fabric.
 8. The method of claim 1, further comprising quantifying a total in-place hydrocarbons from a source contribution of the respective hydrocarbon sample.
 9. The method of claim 1, further comprising: obtaining at least one external sample of stray fluids in one of a well annuli and/or surrounding strata; analyzing at least one external sample for an external geochemical signature comprising a clumped isotope signature and/or position specific isotope signature; comparing the external geochemical signature with the geochemical signatures from the first or second hydrocarbon samples; determining a source interval for the at least one external sample based on the comparison; and developing a mitigation strategy based on the determination.
 10. The method of claim 9, further comprising: introducing an exotic clumped isotope spike into one of the target interval or a wellbore that provides fluid communication to the target interval; analyzing the at least one external sample for the exotic clumped isotope spike; and developing a mitigation strategy based on the analysis.
 11. The method of claim 10, wherein the exotic clumped isotope spike is a form of pure ¹³CD₄.
 12. The method of claim 1, wherein determining whether the hydrocarbons in the sample originated from the target subsurface interval or from a different interval, comprises comparing the determined temperature of the hydrocarbon sample with an expected temperature for the target subsurface interval.
 13. A method for enhancing hydrocarbon production comprising: obtaining one or more samples comprising hydrocarbons from one or more target subsurface intervals of a reservoir, wherein the target subsurface intervals are the subsurface intervals which are intended to be produced during production operations; analyzing the one or more samples for a target geochemical signature, wherein the target geochemical signature comprises a clumped isotope signature and/or a position specific isotope signature for a hydrocarbon compound of interest in the one or more samples; converting the clumped isotope signature and/or the position specific isotope signature of the hydrocarbon compound of interest to a temperature for the one or more samples; obtaining at least one external sample of stray fluids from one of a well annuli and/or surrounding strata; analyzing the at least one external sample for an external geochemical signature comprising a clumped isotope signature and/or position specific isotope signature of a hydrocarbon compound of interest in the external sample; comparing the external geochemical signature with the target geochemical signature; determining a source interval for the at least one external sample based on the comparison; developing a mitigation strategy for the reservoir based on the determination; and producing hydrocarbons from the reservoir based at least in part on the mitigation strategy. 